<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>定位</title>
    <style>
        .box {
            position: absolute;
            top:0px;
            height: 200px;
            width: 200px;
        }

        .xiongda {
            background-color: red;
            z-index: 999;
        }

        .xionger {
            background-color: green;
        }

        .qiangge {
            background-color: blue;
        }
    </style>

</head>
<body>
    <div class="box xiongda">熊大</div>
    <div class="box xionger">熊二</div>
    <div class="box qiangge">光头强</div>

</body>
</html>